GRB 250331D: Swift observation summary

Mission:	Swift/BAT
GRB RA:	48.525°
GRB Dec:	+62.306°
GRB Err:	5.0 arcmin
T0:	2025-03-31 05:49:17 UT
Galactic:	138.69° +3.88°
Galactic N_H:	5.60× 10²¹ cm^-2
Galactic E(B-V):	1.163738

Sun distance:	64.90°
Sun angle:	2.61 [hr] (East of Sun)
Moon distance:	47.20°
Visibility of this field.

Data analysed so far:

ObsID: 00021825001 with 3.0 ks exposure.
ObsID: 00021825002 with 2.3 ks exposure.

Source 2 has been manually confirmed as the GRB afterglow; data for this object are now available through the main GRB results area for this GRB.

About ToO analysis.

Probable afterglow details

A source was found which matches the afterglow criteria.

#	RA (J2000)	Dec (J2000)	Err₉₀¹	Detection Flag²	Dist from Swift/BAT pos	Exposure	Notes	Vizier
2 [details]	03h 14m 37.72s48.65718°	+62° 16′ 59.7″62.28326°	3.5′′	Good	3.9′	8.6 ks	The source is fading with 3.4-σ significance.
Mean XRT rate: 7.4 (±1.5) ×10^-3 ct s^-1 Peak XRT rate: 7.4 (±1.5) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.06 ct s^-1 (XRT equiv count-rate) Mean XRT flux: 3.4 (±0.7) ×10^-13 erg cm^-1s^-1 Peak XRT flux: 3.4 (±0.7) ×10^-13 erg cm^-1s^-1 Products: Spectrum \| Enhanced position \| Expected serendipitous sources: ~0.00×10⁺⁰ [What is this?] Note: this is extragalactic sources only, whereas the GRB trigger is at b=3.88°

¹ Radius, 90% confidence.
² Indicates how likely the source is to be real. See the 2SXPS documentation.
^* The position was enhanced using astrometry derived from the Swift UVOT.
^† The position was astrometrically corrected using the XRT sources and the 2MASS catalogue.

Find an upper limit.

Sources found so far

So far 5 sources have been found in the XRT data. 1 sources match catalogued sources.

#	RA (J2000)	Dec (J2000)	Err₉₀¹	Detection Flag²	Dist from Swift/BAT pos	Exposure	Notes
1 [details]	03h 13m 02.36s48.25985°	+62° 18′ 26.9″62.30748°	4.1′′	Good	7.4′	8.6 ks	Matches known X-ray source: LSXPS J031302.1+621824 (from LSXPS), 4.3″ away. Matches SIMBAD source: ZTF J031302.33+621827.1, 1.8″ away.
Mean XRT rate: 6.2 (±1.1) ×10^-3 ct s^-1 Peak XRT rate: 7.3 (±1.9) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.0×10⁰ ct s^-1 (XRT equiv count-rate) Mean XRT flux: 1.26 (±0.22) ×10^-13 erg cm^-1s^-1 Peak XRT flux: 1.5 (±0.4) ×10^-13 erg cm^-1s^-1 Products: Spectrum \| Enhanced position \| Expected serendipitous sources: ~0.00×10⁺⁰ [What is this?] Note: this is extragalactic sources only, whereas the GRB trigger is at b=3.88°
2 [details]	03h 14m 37.72s48.65718°	+62° 16′ 59.7″62.28326°	3.5′′	Good	3.9′	8.6 ks	The source is fading with 3.4-σ significance.
Mean XRT rate: 7.4 (±1.5) ×10^-3 ct s^-1 Peak XRT rate: 7.4 (±1.5) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.06 ct s^-1 (XRT equiv count-rate) Mean XRT flux: 3.4 (±0.7) ×10^-13 erg cm^-1s^-1 Peak XRT flux: 3.4 (±0.7) ×10^-13 erg cm^-1s^-1 Products: Spectrum \| Enhanced position \| Expected serendipitous sources: ~0.00×10⁺⁰ [What is this?] Note: this is extragalactic sources only, whereas the GRB trigger is at b=3.88°
3 [details]	03h 15m 26.76s48.86152°	+62° 20′ 24.6″62.34017°	7.0′′	Reasonable	9.6′	7.2 ks
Mean XRT rate: 3.01 (+1.21, -0.97) ×10^-3 ct s^-1 Peak XRT rate: 3.01 (+1.21, -0.97) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.04 ct s^-1 (XRT equiv count-rate) Mean XRT flux: 1.3 (+0.5, -0.4) ×10^-13 erg cm^-1s^-1 Peak XRT flux: 1.3 (+0.5, -0.4) ×10^-13 erg cm^-1s^-1 Products: Spectrum \| Expected serendipitous sources: ~0.00×10⁺⁰ [What is this?] Note: this is extragalactic sources only, whereas the GRB trigger is at b=3.88°
4 [details]	03h 15m 04.93s48.77053°	+62° 22′ 24.1″62.37337°	5.9′′	Poor	7.9′	8.6 ks
Mean XRT rate: 1.8 (+0.9, -0.7) ×10^-3 ct s^-1 Peak XRT rate: 1.8 (+0.9, -0.7) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 35176.60 ct s^-1 (XRT equiv count-rate) Mean XRT flux: 1.1 (+0.6, -0.4) ×10^-10 erg cm^-1s^-1 Peak XRT flux: 1.1 (+0.6, -0.4) ×10^-10 erg cm^-1s^-1 Products: Spectrum \| Expected serendipitous sources: ~0.00×10⁺⁰ [What is this?] Note: this is extragalactic sources only, whereas the GRB trigger is at b=3.88°
5 [details]	03h 13m 28.95s48.37064°	+62° 06′ 21.9″62.10607°	6.9′′	Poor	12.7′	7.9 ks
Mean XRT rate: 2.41 (+1.08, -0.76) ×10^-3 ct s^-1 Peak XRT rate: 2.49 (+1.23, -0.93) ×10^-3 ct s^-1 RASS PSPC 3-σ upper limit: 0.04 ct s^-1 (XRT equiv count-rate) Mean XRT flux: 5.7 (+2.5, -1.8) ×10^-14 erg cm^-1s^-1 Peak XRT flux: 5.8 (+2.9, -2.2) ×10^-14 erg cm^-1s^-1 Products: Spectrum \| Expected serendipitous sources: ~0.00×10⁺⁰ [What is this?] Note: this is extragalactic sources only, whereas the GRB trigger is at b=3.88°

¹ Radius, 90% confidence.
² Indicates how likely the source is to be real. See the 1SXPS documentation.
^* The position was enhanced using astrometry derived from the Swift UVOT.
^† The position was astrometrically corrected using the XRT sources and the 2MASS catalogue.

Image

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FITS image.

Exposure map

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FITS exposure map.